Flame-retardant thermoplastic polyurethane

ABSTRACT

The present invention relates to compositions comprising at least one thermoplastic polyurethane, at least melamine cyanurate, at least one first phosphorus-containing flame retardant (F1) selected from the group consisting of derivatives of phosphoric acid and derivatives of phosphonic acid and at least one further phosphorus-containing flame retardant (F2) selected from the group consisting of derivatives of phosphinic acid, and to the use of such a composition for production of cable sheaths.

This application is a National Stage of PCT/EP2015/053192 which wasfiled on Feb. 16, 2015. This application is based upon and claims thebenefit of priority to European Application No. 14156750.3, which wasfiled on Feb. 26, 2014.

The present invention relates to compositions comprising at least onethermoplastic polyurethane, at least melamine cyanurate, at least onefirst phosphorus-containing flame retardant (F1) selected from the groupconsisting of derivatives of phosphoric acid and derivatives ofphosphonic acid and at least one further phosphorus-containing flameretardant (F2) selected from the group consisting of derivatives ofphosphinic acid. The present invention further relates to the use ofsuch compositions for production of cable sheaths.

Cables produced from PVC have the disadvantage of evolving toxic gaseson combustion. Therefore, products based on thermoplastic polyurethanesare being developed, these having lower smoke gas toxicities and havinggood mechanical properties, abrasion resistance and flexibility. Becauseof the inadequate flammability performance, compositions based onthermoplastic polyurethanes are being developed, these comprisingvarious flame retardants.

Flame-retardant thermoplastic polyurethanes find use particularly incable production as cable sheaths. A common requirement here is for thincables having thin cable sheaths which both pass the relevant flametests (e.g. VW1) and have adequate mechanical properties.

In these cases, it is possible to add both halogenated and halogen-freeflame retardants to the thermoplastic polyurethanes (TPUs). Thethermoplastic polyurethanes comprising halogen-free flame retardantsgenerally have the advantage of evolving less toxic and less corrosivesmoke gases when burnt. Halogen-free flame-retardant TPUs are described,for example, in EP 0 617 079 A2, WO 2006/121549 A1 or WO 03/066723 A2.US 2013/0059955 A1 also discloses halogen-free TPU compositionscomprising phosphate-based flame retardants.

US 2013/0081853 A1 relates to compositions, preferably halogen-freeflame-retardant compositions, comprising a TPU polymer and a polyolefin,and also phosphorus-based flame retardants and further additives.According to US 2013/0081853 A1, the compositions have good mechanicalproperties.

Melamine cyanurate has also long been known as a flame retardant forindustrial plastics. It finds wide use especially in polyamides, butalso in polyesters and other plastics such as styrene-based polymers.For instance, WO 97/00916 A describes melamine cyanurate in combinationwith tungstic acid/tungstic salts as flame retardant for aliphaticpolyamides. EP 0 019 768 A1 discloses flameproofing polyamides with amixture of melamine cyanurate and red phosphorus.

According to WO 03/066723, materials comprising only melamine cyanurateas flame retardant, in the case of low wall thicknesses, have neither agood limiting oxygen index (LOI) nor good flame retardancy, determined,for example, by performance in a UL 94 test. WO 2006/121549 A1 alsodescribes materials comprising, as flame retardant, a combination ofmelamine polyphosphate, phosphinate and borate. These materials doattain high LOI values at low wall thicknesses, but do not attain goodresults in the UL 94 test.

There are also various known thermoplastic polyurethanes which comprise,as flame retardants, combinations of melamine cyanurate in conjunctionwith phosphorus compounds. EP 0 617 079 A2 and DE 102 24 340 A1 disclosematerials that exhibit good performance in the UL 94 test (particularlyin the UL 94V test), but at the same time have low LOI values.

For example, materials which comprise, as flame retardants, combinationsof melamine cyanurate with phosphonic esters and phosphonic esters havegood results in UL 94V tests, but very low LOI values, for example <25%.Such combinations of melamine cyanurate with phosphoric esters andphosphonic esters are inadequate as flame retardants particularly in thecase of sheaths of thin cables. For various flame retardancyapplications, a high LOI value is required in standards, for example inDIN EN 45545.

By contrast, very high LOI values (>30%) can be achieved withcombinations of melamine cyanurate with phosphinates, but not goodresults in the UL 94V test. Corresponding materials are disclosed, forexample, by U.S. Pat. Nos. 6,207,736 B1, 6,255,371, 6,365,071 B1,6,509,401 B1 and 6,547,992 B1.

Accordingly, the compositions known from the prior art either do notexhibit adequate mechanical properties or have only inadequateflammability properties, for example flame retardancy and performance,in the UL 94V test.

Proceeding from the prior art, it was accordingly an object of thepresent invention to provide flame-retardant thermoplastic polyurethaneswhich have good mechanical properties, exhibit good flame retardancyproperties and simultaneously have good mechanical and chemicalstability.

According to the invention, this object is achieved by a compositioncomprising at least one thermoplastic polyurethane, at least melaminecyanurate, at least one first phosphorus-containing flame retardant (F1)selected from the group consisting of derivatives of phosphoric acid andderivatives of phosphonic acid and at least one furtherphosphorus-containing flame retardant (F2) selected from the groupconsisting of derivatives of phosphinic acid.

The compositions of the invention comprise at least one thermoplasticpolyurethane and also melamine cyanurate and a combination of twophosphorus-containing flame retardants (F1) and (F2).

It has been found that, surprisingly, the compositions of the inventionhave properties improved over the compositions known from the prior art,for example elevated flame retardancy.

The compositions of the invention comprise melamine cyanurate. It hasbeen found that, surprisingly, the compositions of the invention have anoptimized profile of properties as a result of the combination of thecomponents of the invention, especially for use as cable sheathing.

Melamine cyanurate in the context of this application is understood tomean, inter alia, all standard commercial and commercially availablesolid, preferably particulate, product qualities. Examples of theseinclude Melapur MC 25 (BASF SE) and Budit 315 (Budenheim).

According to the invention, melamine cyanurate is preferably used in theform of a 1:1 salt of melamine and cyanuric acid. The melamine excesshere is, for example, less than 0.2%, preferably less than 0.15%,further preferably less than 0.1%. According to the invention, thecyanuric acid excess is, for example, less than 0.25%, preferably lessthan 0.2%, further preferably less than 0.15%.

In the context of the present invention, it is likewise possible thatthe melamine cyanurate used has been treated, for example with anorganic compound. Corresponding materials are known in principle fromthe prior art.

The melamine cyanurate which is suitable in accordance with theinvention preferably consists of particles typically having a meanparticle diameter of 0.1 μm to 100 μm, preferably 0.5 μm to 60 μm, morepreferably 1 μm to 10 μm. The particle size distribution in the contextof the present invention may be monomodal or else multimodal, forexample bimodal.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the melamine cyanurate has aparticle size in the range from 0.1 to 100 μm.

Melamine cyanurate is present in suitable amounts in the composition ofthe invention. For example, the proportion of melamine cyanurate in thecomposition is in the range from 20% to 40% by weight, based on theoverall composition, preferably composition in the range from 25% to 35%by weight, based on the overall composition, especially composition inthe region of about 30% by weight, based on the overall composition.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the proportion of the melaminecyanurate in the composition is in the range from 20% to 40% by weightbased on the overall composition.

The sum total of the components of the composition is 100% by weight ineach case.

The composition of the invention further comprises at least onethermoplastic polyurethane. Thermoplastic polyurethanes are known inprinciple. They are typically prepared by reacting the components (a)isocyanates and (b) compounds reactive toward isocyanates and optionally(c) chain extenders, optionally in the presence of at least one (d)catalyst and/or (e) customary auxiliaries and/or additives. Thecomponents (a) isocyanate, (b) compounds reactive toward isocyanates,(c) chain extenders are also referred to, individually or collectively,as formation components.

In the context of the present invention, the isocyanates and compoundsreactive toward isocyanates which are customarily used are suitable inprinciple.

Organic isocyanates (a) used are preferably aliphatic, cycloaliphatic,araliphatic and/or aromatic isocyanates, further preferably tri-,tetra-, penta-, hexa-, hepta- and/or octamethylene diisocyanate,2-methylpentamethylene 1,5-diisocyanate, 2-ethylbutylene1,4-diisocyanate, pentamethylene 1,5-diisocyanate, butylene1,4-diisocyanate,1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophoronediisocyanate, IPDI), 1,4- and/or 1,3-bis(isocyanatomethyl)cyclohexane(HXDI), cyclohexane 1,4-diisocyanate, 1-methylcyclohexane 2,4- and/or2,6-diisocyanate and/or dicyclohexylmethane 4,4′-, 2,4′- and2,2′-diisocyanate, diphenylmethane 2,2′-, 2,4′- and/or 4,4′-diisocyanate(MDI), naphthylene 1,5-diisocyanate (NDI), tolylene 2,4- and/or2,6-diisocyanate (TDI), diphenylmethane diisocyanate, 3,3′-dimethyldiphenyl diisocyanate, 1,2-diphenylethane diisocyanate and/or phenylenediisocyanate. Particular preference is given to using 4,4′-MDI.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the thermoplastic polyurethaneis based on diphenylmethane diisocyanate (MDI).

Compounds (b) reactive toward isocyanates used may in principle be anysuitable compounds known to those skilled in the art. As compound (b)reactive toward isocyanates, in accordance with the invention, at leastone diol is used.

It is possible here in the context of the present invention to use anysuitable diols, for example polyether dials or polyester dials ormixtures of two or more thereof.

In principle, it is possible in accordance with the invention to use anysuitable polyester diols, the term “polyester diol” in the context ofthe present invention also comprising polycarbonatediols.

In one embodiment of the present invention, a polycarbonatediol or apolytetrahydrofuran polyol is used. Suitable polytetrahydrofuran polyolshave, for example, a molecular weight in the range from 500 to 5000g/mol, preferably 500 to 2000 g/mol, more preferably 800 to 1200 g/mol.

Suitable polycarbonatediols are, for example, polycarbonatediols basedon alkanediols. Suitable polycarbonatediols are strictly difunctionalOH-functional polycarbonatediols, preferably strictly difunctionalOH-functional aliphatic polycarbonatediols. Suitable polycarbonatediolsare based, for example, on butane-1,4-diol, pentane-1,5-diol orhexane-1,6-diol, especially butane-1,4-diol, pentane-1,5-diol,hexane-1,6-diol, 3-methylpentane-1,5-diol or mixtures thereof, morepreferably butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol ormixtures thereof. Preference is given in the context of the presentinvention to using polycarbonatediols based on butane-1,4-diol andhexane-1,6-diol, polycarbonatediols based on pentane-1,5-diol andhexane-1,6-diol, polycarbonatediols based on hexane-1,6-diol, andmixtures of two or more of these polycarbonatediols.

The compositions of the invention preferably comprise at least onethermoplastic polyurethane selected from the group consisting ofthermoplastic polyurethanes based on at least one diisocyanate and atleast one polycarbonatediol and thermoplastic polyurethanes based on atleast one diisocyanate and polytetrahydrofuran polyol. Accordingly, thepolyurethanes present in the compositions of the invention are preparedusing, as component (b), at least one polycarbonatediol or apolytetrahydrofuran polyol.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the thermoplastic polyurethaneis selected from the group consisting of thermoplastic polyurethanesbased on at least one diisocyanate and at least one polycarbonatediol,and thermoplastic polyurethanes based on at least one diisocyanate andpolytetrahydrofuran polyol.

In a further embodiment, the present invention also relates to acomposition as described above, wherein the thermoplastic polyurethaneis a thermoplastic polyurethane based on at least one diisocyanate andat least one polycarbonatediol. Preferably, the polycarbonatediols usedhave a number-average molecular weight Mn in the range from 500 to 4000g/mol, determined via GPC, preferably in the range from 650 to 3500g/mol, determined via GPC, more preferably in the range from 800 to 3000g/mol, determined via GPC.

The present invention further relates, in a further embodiment, also toa composition as described above, wherein the thermoplastic polyurethaneis a thermoplastic polyurethane based on at least one diisocyanate andat least one polycarbonatediol and the at least one polycarbonatediol isselected from the group consisting of polycarbonatediols based onbutane-1,4-diol and hexane-1,6-diol, polycarbonatediols based onpentane-1,5-diol and hexane-1,6-diol, polycarbonatediols based onhexane-1,6-diol, and mixtures of two or more of thesepolycarbonatediols. Further preferred are copolycarbonatediols based onthe diols pentane-1,5-diol and hexane-1,6-diol, preferably having amolecular weight Mn of about 2000 g/mol.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the polycarbonatediol has anumber-average molecular weight Mn in the range from 500 to 4000 g/mol,determined via GPC, preferably in the range from 1000 to 3500 g/mol,determined via GPC, further preferably in the range from 1500 to 3000g/mol, determined via GPC.

Chain extenders (c) used may preferably be aliphatic, araliphatic,aromatic and/or cycloaliphatic compounds having a molecular weight of0.05 kg/mol to 0.499 kg/mol, preferably difunctional compounds, forexample diamines and/or alkanediols having 2 to 10 carbon atoms in thealkylene radical, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-and/or decaalkylene glycols having 3 to 8 carbon atoms, especially1,2-ethylene glycol, propane-1,3-diol, butane-1,4-diol, hexane-1,6-diol,preferably corresponding oligo- and/or polypropylene glycols, where itis also possible to use mixtures of the chain extenders. Preferably, thecompounds (c) have only primary hydroxyl groups; most preferred isbutane-1,4-diol.

Catalysts (d) which accelerate particularly the reaction between the NCOgroups of the diisocyanates (a) and the hydroxyl groups of the compound(b) reactive toward isocyanates and the chain extender (c), in apreferred embodiment, are tertiary amines, especially triethylamine,dimethylcyclohexylamine, N-methylmorpholine, N,N′-dimethylpiperazine,2-(dimethylaminoethoxy)ethanol, diazabicyclo[2.2.2]octane; in anotherpreferred embodiment, these are organic metal compounds such as titanicesters, iron compounds, preferably iron(III) acetylacetonate, tincompounds, preferably tin diacetate, tin dioctoate, tin dilaurate or thedialkyltin salts of aliphatic carboxylic acids, preferably dibutyltindiacetate, dibutyltin dilaurate, or bismuth salts in which bismuth ispreferably in the 2 or 3 oxidation state, especially 3. Preference isgiven to salts of carboxylic acids. Carboxylic acids used are preferablycarboxylic acids having 6 to 14 carbon atoms, more preferably having 8to 12 carbon atoms. Examples of suitable bismuth salts are bismuth(III)neodecanoate, bismuth 2-ethylhexanoate and bismuth octanoate.

The catalysts (d) are preferably used in amounts of 0.0001 to 0.1 partby weight per 100 parts by weight of the compound (b) reactive withisocyanates. Preference is given to using tin catalysts, especially tindioctoate.

As well as catalysts (d), it is also possible to add customaryauxiliaries (e) to the formation components (a) to (c). Examples includesurface-active substances, fillers, further flame retardants, nucleatingagents, oxidation stabilizers, gliding and demolding aids, dyes andpigments, optionally stabilizers, for example against hydrolysis, light,heat or discoloration, inorganic and/or organic fillers, reinforcingagents and plasticizers. Suitable auxiliaries and additives can befound, for example, in the Kunststoffhandbuch [Plastics Handbook],volume VII, published by Vieweg and Höchtlen, Carl Hanser Verlag, Munich1966 (p. 103-113).

Suitable preparation processes for thermoplastic polyurethanes aredisclosed, for example, in EP 0 922 552 A1, DE 101 03 424 A1 or WO2006/072461 A1. The preparation is typically effected in a belt systemor a reaction extruder, but can also be effected on the laboratoryscale, for example in a manual casting method. Depending on the physicalproperties of the components, they are all mixed directly with oneanother or individual components are premixed and/or prereacted, forexample to give prepolymers, and only then subjected to polyaddition. Ina further embodiment, a thermoplastic polyurethane is first preparedfrom the formation components, optionally together with catalyst, intowhich auxiliaries may optionally also be incorporated. In that case, atleast one flame retardant is introduced into this material anddistributed homogeneously. The homogeneous distribution is preferablyeffected in an extruder, preferably in a twin-shaft extruder. To adjustthe hardness of the TPUs, the amounts used of formation components (b)and (c) can be varied within relatively broad molar ratios, typicallywith rising hardness as the content of chain extender (c) increases.

For preparation of thermoplastic polyurethanes, for example those havinga Shore A hardness of less than 95, preferably of 95 to 80 Shore A, morepreferably about 85 A, it is possible, for example, to use theessentially difunctional polyhydroxyl compounds (b) and chain extenders(c) advantageously in molar ratios of 1:1 to 1:5, preferably 1:1.5 to1:4.5, such that the resulting mixtures of the formation components (b)and (c) have a hydroxyl equivalent weight of greater than 200 andespecially of 230 to 450, whereas, for preparation of harder TPUs, forexample those having a Shore A hardness of greater than 98, preferablyof 55 to 75 Shore D, the molar ratios of (b):(c) are in the range from1:5.5 to 1:15, preferably from 1:6 to 1:12, such that the mixtures of(b) and (c) obtained have a hydroxyl equivalent weight of 110 to 200,preferably of 120 to 180.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the thermoplastic polyurethanehas a Shore hardness in the range from 80 A to 100 A, determined inaccordance with DIN 53505.

To prepare the thermoplastic polyurethanes of the invention, theformation components (a), (b) and (c) are preferably reacted in thepresence of catalysts (d) and optionally auxiliaries and/or additives(e) in such amounts that the ratio of equivalents of NCO groups in thediisocyanates (a) to the sum total of the hydroxyl groups in theformation components (b) and (c) is 0.9 to 1.1:1, preferably 0.95 to1.05:1 and especially about 0.96 to 1.0:1.

The composition of the invention comprises the at least onethermoplastic polyurethane in an amount in the range from 30% by weightto 75% by weight, based on the overall composition, especially in therange from 35% by weight to 75% by weight, based on the overallcomposition, preferably in the range from 40% by weight to 70% byweight, further preferably in the range from 45% by weight to 65% byweight and especially preferably in the range from 50% by weight to 60%by weight, based in each case on the overall composition.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the proportion of thethermoplastic polyurethane in the composition is in the range from 30%by weight to 75% by weight based on the overall composition.

The sum of all components of each composition adds up to 100% by weight.

Preference is given in accordance with the invention to preparingthermoplastic polyurethanes in which the thermoplastic polyurethane hasa mean molecular weight (M_(w)) in the range from 50 000 to 500 000 Da.The upper limit for the mean molecular weight (M_(w)) of thethermoplastic polyurethanes is generally determined by theprocessibility, and also the spectrum of properties desired. Furtherpreferably, the thermoplastic polyurethane has a mean molecular weight(M_(w)) in the range from 75 000 to 400 000 Da, especially preferably inthe range from 100 000 to 300 000 Da.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the thermoplastic polyurethanehas a mean molecular weight (M_(w)) in the range from 50 000 to 500 000Da.

The compositions of the invention comprise, as well as the at least onethermoplastic polyurethane and melamine cyanurate, a combination of twophosphorus-containing flame retardants (F1) and (F2). The compositionsof the invention comprise at least one first phosphorus-containing flameretardant (F1) selected from the group consisting of derivatives ofphosphoric acid and derivatives of phosphonic acid and at least onefurther phosphorus-containing flame retardant (F2) selected from thegroup consisting of derivatives of phosphinic acid.

In a further preferred embodiment, the phosphorus-containing flameretardant (F1) is liquid at 21° C.

Preferably, the flame retardant (F1) selected from the group consistingof derivatives of phosphoric acid and derivatives of phosphonic acidcomprises salts having an organic or inorganic cation or organic esters.Organic esters are derivatives of the phosphorus-containing acids inwhich at least one oxygen atom bonded directly to the phosphorus hasbeen esterified with an organic radical. In a preferred embodiment, theorganic ester is an alkyl ester, and in another preferred embodiment anaryl ester. More preferably, all hydroxyl groups of the correspondingphosphorus-containing acid have been esterified.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the phosphorus-containing flameretardant (F1) is a phosphoric ester.

Organic phosphate esters are preferred, particularly the triesters ofphosphoric acid, such as trialkyl phosphates and especially triarylphosphates, for example triphenyl phosphate.

Preference is given in accordance with the invention to using, as flameretardants for the thermoplastic polyurethanes, phosphoric esters of thegeneral formula (I)

where R represents optionally substituted alkyl, cycloalkyl or phenylgroups and n=1 to 15.

If R in the general formula (I) is an alkyl radical, especially usefulare those alkyl radicals having 1 to 8 carbon atoms. One example ofcycloalkyl groups is the cyclohexyl radical. Preference is given tousing those phosphoric esters of the general formula (I) in whichR=phenyl or alkyl-substituted phenyl. n in the general formula (I) isespecially 1 or is preferably in the range from about 3 to 6. Examplesof preferred phosphoric esters of the general formula (I) includephenylene 1,3-bis(diphenyl) phosphate, phenylene 1,3-bis(dixylenyl)phosphate and the corresponding oligomeric products having a meanoligomerization level of n=3 to 6. A preferred resorcinol is resorcinolbis(diphenyl phosphate) (RDP), which is typically present in oligomers.

Further preferred phosphorus-containing flame retardants (F1) arebisphenol A bis(diphenyl phosphate) (BDP), which is typically inoligomeric form, and diphenyl cresyl phosphate (DPK).

Accordingly, the present invention also relates, in a furtherembodiment, to a composition as described above, wherein thephosphorus-containing flame retardant (F1) is selected from the groupconsisting of resorcinol bis(diphenyl phosphate) (RDP), bisphenol Abis(diphenyl phosphate) (BDP) and diphenyl cresyl phosphate (DPK).

In a further embodiment, the present invention also relates to acomposition as described above, wherein the phosphorus-containing flameretardant (F1) is resorcinol bis(diphenyl phosphate) (RDP).

The organic phosphonates are salts with an organic or inorganic cationor the esters of phosphonic acid. Preferred esters of phosphonic acidare the diesters of alkyl- or phenylphosphonic acids. Examples of thephosphonic esters for use as flame retardants in accordance with theinvention include the phosphonates of the general formula (II)

where

-   R¹ represents optionally substituted alkyl, cycloalkyl or phenyl    groups, where the two R¹ radicals may also be joined to one another    in a cycle, and-   R² is an optionally substituted alkyl, cycloalkyl or phenyl radical.

Particularly suitable are cyclic phosphonates, for example

with R²═CH₃ and C₆H₅, which derive from pentaerythritol, or

-   -   with R²═CH₃ and C₆H₅, which derive from neopentyl glycol, or

-   -   with R²═CH₃ and C₆H₅, which derive from catechol, or else

with R²=an unsubstituted or else substituted phenyl radical.

The proportion of the flame retardant (F1) in the composition of theinvention is, for example, in the range from 2% to 15% by weight, basedon the overall composition, preferably in the range from 3% to 10% byweight, based on the overall composition, especially in the range from5% to 8% by weight, based on the overall composition.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the proportion of the flameretardant (F1) is in the range from 2% to 15% based on the overallcomposition.

Preferably, the flame retardant (F2) selected from derivatives ofphosphinic acid comprises salts with an organic or inorganic cation ororganic esters. Organic esters are derivatives of phosphinic acid inwhich at least one oxygen atom bonded directly to the phosphorus hasbeen esterified with an organic radical. In a preferred embodiment, theorganic ester is an alkyl ester, and in another preferred embodiment anaryl ester. More preferably, all hydroxyl groups of the phosphinic acidhave been esterified.

Phosphinic esters have the general formula R¹R²(P═O)OR³ where all threeorganic groups R¹, R² and R³ may be the same or different. The R¹, R²and R³ radicals are either aliphatic or aromatic and have 1 to 20 carbonatoms, preferably 1 to 10 and further preferably 1 to 3. Preferably, atleast one of the radicals is aliphatic, preferably all the radicals arealiphatic, and most preferably R¹ and R² are ethyl radicals. Furtherpreferably, R³ is also an ethyl radical or a methyl radical. In afurther preferred embodiment, R¹, R² and R³ are simultaneously ethylradical or methyl radicals.

Preference is also given to phosphinates, i.e. the salts of phosphinicacid. The R¹ and R² radicals are either aliphatic or aromatic and have 1to 20 carbon atoms, preferably 1 to 10 and further preferably 1 to 3.Preferably, at least one of the radicals is aliphatic, preferably allthe radicals are aliphatic, and most preferably R¹ and R² are ethylradicals. Preferred salts of phosphinic acids are aluminum salts,calcium salts or zinc salts, further preferably aluminum salts or zincsalts. A preferred embodiment is diethylaluminum phosphinate.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the phosphorus-containing flameretardant (F2) is a phosphinate.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the phosphinate is selected fromthe group consisting of aluminum phosphinates and zinc phosphinates.

The proportion of the flame retardant (F2) in the composition of theinvention is, for example, in the range from 3% to 15% by weight, basedon the overall composition, especially 5% to 15% by weight, based on theoverall composition, preferably in the range from 7% to 13% by weight,based on the overall composition, especially in the range from 9% to 11%by weight, based on the overall composition.

In a further embodiment, the present invention therefore relates to acomposition as described above, wherein the proportion of the flameretardant (F2) in the composition is in the range from 3% to 15% byweight based on the overall composition.

In one embodiment, for preparation of the compositions of the invention,thermoplastic polyurethane, melamine cyanurate and flame retardants (F1)and (F2) are processed in one step. In other preferred embodiments, forpreparation of the compositions of the invention, a reaction extruder, abelt system or other suitable apparatus is firstly used to prepare athermoplastic polyurethane, preferably in pellet form, into whichmelamine cyanurate and the flame retardants (F1) and (F2) are thenintroduced in at least one further step, or else two or more steps.

The mixing of the thermoplastic polyurethane with the other componentsis effected in a mixing unit which is preferably an internal kneader oran extruder, preferably a twin-shaft extruder. In a preferredembodiment, at least one flame retardant introduced into the mixing unitin the at least one further step is in liquid form, i.e. in liquid format a temperature of 21° C. In another preferred embodiment of the use ofan extruder, the flame retardant introduced is at least partly liquid ata temperature that exists behind the intake point in flow direction ofthe material charge in the extruder.

According to the invention, the composition may comprise further flameretardants, for example including phosphorus-containing flameretardants. Preferably, the composition of the invention, however, asidefrom the melamine cyanurate and the phosphorus-containing flameretardants (F1) and (F2), does not comprise any further flameretardants.

The combination of the various flame retardants optimizes mechanicalproperties and flame retardancy properties in accordance with theinvention.

In this case, the mass ratio of the sum total of thephosphorus-containing flame retardants and (F2) present in thecomposition to the melamine cyanurate present in the composition, inaccordance with the invention, is in the range from 1:3 to 1:1, forexample in the region of 1:2.

Accordingly, the present invention, in a further embodiment, alsorelates to a composition comprising at least one thermoplasticpolyurethane, at least melamine cyanurate, at least one firstphosphorus-containing flame retardant (F1) selected from the groupconsisting of derivatives of phosphoric acid and derivatives ofphosphonic acid and at least one further phosphorus-containing flameretardant (F2) selected from the group consisting of derivatives ofphosphinic acid, wherein

-   -   the proportion of the thermoplastic polyurethane in the        composition is in the range from 30% to 75% by weight,    -   the proportion of the melamine cyanurate in the composition is        in the range from 20% to 40% by weight,    -   the proportion of the flame retardant (F2) in the composition is        in the range from 3% to 15% by weight, and    -   the proportion of the flame retardant (F1) is in the range from        2% to 15% by weight, based in each case on the overall        composition, where the sum total of the components of the        composition is 100% by weight.

According to the invention, the composition may comprise furtherconstituents, for example standard auxiliaries and additives forthermoplastic polyurethanes. Preferably, the composition, aside from themelamine cyanurate, the at least one phosphorus-containing flameretardant (F1) and the at least one phosphorus-containing flameretardant (F2), does not comprise any further flame retardants. Furtherpreferably, the composition of the invention comprises melaminecyanurate, exactly one phosphorus-containing flame retardant (F1)selected from the group consisting of derivatives of phosphoric acid andderivatives of phosphonic acid and exactly one phosphorus-containingflame retardant (F2) selected from the group consisting of derivativesof phosphinic acid.

The present invention also relates to the use of the composition of theinvention comprising at least one flame-retardant thermoplasticpolyurethane as described above for production of coatings, dampingelements, bellows, films or fibers, shaped bodies, floors for buildingsand transport, nonwovens, preferably seals, rollers, shoe soles, hoses,cables, cable connectors, cable sheaths, cushions, laminates, profiles,belts, saddles, foams, plug connectors, trailing cables, solar modules,automobile trim. Preference is given to the use for production of cablesheaths. The production is preferably effected from pellets, byinjection molding, calendering, powder sintering or extrusion and/or byadditional foaming of the composition of the invention.

Accordingly, the present invention also relates to the use of acomposition comprising at least one thermoplastic polyurethane, at leastmelamine cyanurate, at least one first phosphorus-containing flameretardant (F1) selected from the group consisting of derivatives ofphosphoric acid and derivatives of phosphonic acid and at least onefurther phosphorus-containing flame retardant (F2) selected from thegroup consisting of derivatives of phosphinic acid as described abovefor production of cable sheaths.

Further embodiments of the present invention can be inferred from theclaims and the examples. It will be appreciated that the features of theinventive subject matter/process or of the inventive uses which havebeen mentioned above and those elucidated below can be used not only inthe combination specified in each case but also in other combinations,without leaving the scope of the invention. For example, the combinationof a preferred feature with an especially preferred feature or of afeature which is not characterized any further with an especiallypreferred feature, etc., is implicitly also encompassed even if thiscombination is not mentioned explicitly.

Listed hereinafter are illustrative embodiments of the presentinvention, though these do not restrict the present invention. Moreparticularly, the present invention also encompasses those embodimentswhich arise from the dependency references and hence combinationsspecified hereinafter.

-   1. A composition comprising at least one thermoplastic polyurethane,    at least melamine cyanurate, at least one first    phosphorus-containing flame retardant (F1) selected from the group    consisting of derivatives of phosphoric acid and derivatives of    phosphonic acid and at least one further phosphorus-containing flame    retardant (F2) selected from the group consisting of derivatives of    phosphinic acid.-   2. The composition according to embodiment 1, wherein the    phosphorus-containing flame retardant (F2) is a phosphinate.-   3. The composition according to embodiment 2, wherein the    phosphinate is selected from the group consisting of aluminum    phosphinates and zinc phosphinates.-   4. The composition according to any of embodiments 1 to 3, wherein    the phosphorus-containing flame retardant (F1) is a phosphoric    ester.-   5. The composition according to any of embodiments 1 to 4, wherein    the flame retardant (F1) is selected from the group consisting of    resorcinol bis(diphenyl phosphate) (RDP), bisphenol A bis(diphenyl    phosphate) (BDP) and diphenyl cresyl phosphate (DPK).-   6. The composition according to any of embodiments 1 to 5, wherein    the melamine cyanurate has a particle size in the range from 0.1 to    100 μm.-   7. The composition according to any of embodiments 1 to 6, wherein    the thermoplastic polyurethane is selected from the group consisting    of thermoplastic polyurethanes based on at least one diisocyanate    and at least one polycarbonatediol, and thermoplastic polyurethanes    based on at least one diisocyanate and polytetrahydrofuran polyol.-   8. The composition according to any of embodiments 1 to 7, wherein    the thermoplastic polyurethane has a mean molecular weight (M_(w))    in the range from 50 000 to 500 000 Da.-   9. The composition according to any of embodiments 1 to 8, wherein    the thermoplastic polyurethane is based on diphenylmethane    diisocyanate (MDI).-   10. The composition according to any of embodiments 1 to 9, wherein    the thermoplastic polyurethane has a Shore hardness in the range    from 80 A to 100 A, determined in accordance with DIN 53505.-   11. The composition according to any of embodiments 1 to 10, wherein    the proportion of the thermoplastic polyurethane in the composition    is in the range from 30% by weight to 75% by weight based on the    overall composition.-   12. The composition according to any of embodiments 1 to 11, wherein    the proportion of the melamine cyanurate in the composition is in    the range from 20% to 40% by weight based on the overall    composition.-   13. The composition according to any of embodiments 1 to 12, wherein    the proportion of the flame retardant (F2) in the composition is in    the range from 3% to 15% by weight based on the overall composition.-   14. The composition according to any of embodiments 1 to 18, wherein    the proportion of the flame retardant (F1) is in the range from 2%    to 15% by weight based on the overall composition.-   15. The use of a composition according to any of embodiments 1 to 14    for production of cable sheaths.-   16. A composition comprising at least one thermoplastic    polyurethane, at least melamine cyanurate, at least one first    phosphorus-containing flame retardant (F1) selected from the group    consisting of derivatives of phosphoric acid and derivatives of    phosphonic acid and at least one further phosphorus-containing flame    retardant (F2) selected from the group consisting of derivatives of    phosphinic acid,    -   wherein the phosphinate is selected from the group consisting of        aluminum phosphinates and zinc phosphinates and    -   wherein the flame retardant (F1) is selected from the group        consisting of resorcinol bis(diphenyl phosphate) (RDP),        bisphenol A bis(diphenyl phosphate) (BDP) and diphenyl cresyl        phosphate (DPK).-   17. A composition comprising at least one thermoplastic    polyurethane, at least melamine cyanurate, at least one first    phosphorus-containing flame retardant (F1) selected from the group    consisting of derivatives of phosphoric acid and derivatives of    phosphonic acid and at least one further phosphorus-containing flame    retardant (F2) selected from the group consisting of derivatives of    phosphinic acid,    -   wherein the proportion of the thermoplastic polyurethane in the        composition is in the range from 30% to 75% by weight based on        the overall composition,    -   wherein the proportion of the melamine cyanurate in the        composition is in the range from 20% to 40% by weight based on        the overall composition, wherein the proportion of the flame        retardant (F2) in the composition is in the range from 3% to 15%        by weight based on the overall composition, and    -   wherein the proportion of the flame retardant (F1) is in the        range from 2% to 15% by weight based on the overall composition,        and    -   where the sum total of the components of the composition is 100%        by weight.-   18. The composition according to any of embodiments 1 to 13, wherein    the proportion of the flame retardant (F1) is in the range from 2%    to 15% by weight based on the overall composition.

The examples which follow serve to illustrate the invention, but are inno way restrictive with respect to the subject matter of the presentinvention.

EXAMPLES

The examples show the improved flame retardancy of the compositions ofthe invention, the good mechanical properties and the lower smoke gasdensity.

1. Feedstocks

-   -   Elastollan 1185A10: TPU of Shore hardness 85 A from BASF        Polyurethanes GmbH, Elastogranstrasse 60, 49448 Lemförde, based        on polytetrahydrofuran polyol (PTHF) having a molecular weight        of 1000, butane-1,4-diol, MDI.    -   Melapur MC 15 ED: Melamine cyanurate        (1,3,5-triazine-2,4,6(1H,3H,5H)-trione, compound with        1,3,5-triazine-2,4,6-triamine (1:1)), CAS #: 37640-57-6, BASF        SE, 67056 Ludwigshafen, GERMANY, particle size D99%<1=50 μm,        D50%<=4.5 μm, water content    -   Fyrolflex RDP: Resorcinol bis(diphenylphosphate), CAS #:        125997-21-9, Supresta Netherlands B.V., Office Park De Hoef,        Hoefseweg 1, 3821 AE Amersfoort, the Netherlands, viscosity at        25° C.=700 mPas, acid number <0.1 mg KOH/g, water content    -   Disflamoll DPK: Cresyl diphenyl phosphate, CAS #: 026444-49-5,        LANXESS Deutschland GmbH, 51369 Leverkusen, Germany, acid        number<0.1 mg KOH/g, water content % (w/w)<0.1.    -   Exolit OP 1230: Aluminum diethylphosphinate, CAS#: 225789-38-8,        Clariant Produkte (Deutschland) GmbH, Chemiepark Knapsack, 50351        Hürth, water content % (w/w)<0.2, average particle size (D50)        20-40 μm.        2. Production of the Mixtures    -   Table 1 below lists compositions in which the individual        constituents are stated in parts by weight (PW). The mixtures        were each produced with a Berstorff ZE 40 A twin-screw extruder        having a screw length of 35 D divided into 10 barrel sections.

TABLE 1 Mixtures I II III* IV* 1185A10 55 55 60 59 Melapur MC 15ED 30 3040 33 Fyrolflex RDP 5 8 Disflamoll DPK 5 Exolit OP 1230 10 10 Mechanicalproperties MFR 200° C./21.6 kg [g/10 min] DIN EN ISO 1133 100 70 50 40Density [g/cm³] DIN EN ISO 1183-1, A 1.27 1.26 1.29 1.27 Shore hardness[A] DIN 53505 91 91 94 91 TS [MPa] DIN EN ISO 527 17 17 15 25 EB [%] DINEN ISO 527 540 540 400 600 TPR [kN/m] DIN ISO 34-1, B (b) 65 58 60 65Abrasion [mm³] DIN ISO 4649 85 72 54 40 Flame tests VW1 testconducted/passed 3/3 3/3 0/3 1/3 UL 94V UL 94V, 1.6 mm pass pass failpass LOI [%] ISO 4589-2, 1.6 mm 30 30 24 23 *comparative example3. Mechanical Properties

-   -   The mixtures were extruded with an Arenz single-screw extruder        having a three-zone screw with a mixing section (screw ratio        1:3) to give films having a thickness of 1.6 mm. The parameters        measured were MFR of the pellets used, density, Shore hardness,        tensile strength, tear propagation resistance and elongation at        break of the corresponding test specimens.        4. Flame Retardancy    -   In order to assess flame retardancy, a test specimen having a        thickness of 1.6 mm is tested in accordance with UL 94V (UL        Standard for Safety for Tests for Flammability of Plastic        Materials for Parts in Devices and Appliances).    -   In order to assess flame retardancy, cables were produced on a        conventional extrusion line (smooth tube extruder, extruder        diameter 45 mm) for cable insulation and cable sheathing. A        conventional three-zone screw with a compression ratio of 2.5:1        was employed.    -   First of all, the cores (8 twisted individual wires) were        insulated with the respective mixtures with 0.1 mm of the        respective mixtures in a tubular method. The diameter of the        insulated cores was 1.0 mm. Three of these cores were stranded        and a shell (shell thickness 1 mm) was applied by extrusion in a        tubular method. The external diameter of the overall cable was 5        mm.    -   Then a VW 1 test (UL Standard 1581, § 1080-VW-1 (vertical        specimen) flame test) was conducted on the cables. The test was        conducted on 3 cables in each case.

The invention claimed is:
 1. A composition, comprising: at least onethermoplastic polyurethane; at least one melamine cyanurate; at leastone first phosphorus-containing flame retardant (F1) selected from thegroup consisting of a phosphoric acid compound, a phosphonic acidcompound, and derivatives thereof; at least one furtherphosphorus-containing flame retardant (F2) comprising a phosphinic acidcompound or derivative thereof, wherein: the phosphorus-containing flameretardant (F1) comprises a phosphoric ester; the phosphorus-containingflame retardant (F2) comprises a phosphinate; and a proportion of themelamine cyanurate in the composition is from 25% to 40% by weight basedon the overall composition.
 2. The composition according to claim 1,wherein the phosphinate is selected from the group consisting of analuminum phosphinate and a zinc phosphinate.
 3. The compositionaccording to claim 1, wherein the flame retardant (F1) is selected fromthe group consisting of resorcinol bis(diphenyl phosphate) (RDP),bisphenol A bis(diphenyl phosphate) (BDP) and diphenyl cresyl phosphate(DPK).
 4. The composition according to claim 1, wherein the melaminecyanurate has a particle size in the range from 0.1 to 100 μm.
 5. Thecomposition according to claim 1, wherein: the phosphinate is selectedfrom the group consisting of an aluminum phosphinate and a zincphosphinate; the flame retardant (F1) is selected from the groupconsisting of resorcinol bis(diphenyl phosphate) (RDP), bisphenol Abis(diphenyl phosphate) (BDP) and diphenyl cresyl phosphate (DPK); andthe melamine cyanurate has a particle size in the range from 0.1 to 100μm.
 6. The composition according to claim 1, wherein the thermoplasticpolyurethane is selected from the group consisting of a thermoplasticpolyurethane based on at least one diisocyanate and at least onepolycarbonatediol, and a thermoplastic polyurethane based on at leastone diisocyanate and polytetrahydrofuran polyol.
 7. The compositionaccording to claim 1, wherein the thermoplastic polyurethane has a meanmolecular weight (M_(w)) in the range from 50,000 to 500,000 Da.
 8. Thecomposition according to claim 1, wherein the thermoplastic polyurethaneis based on diphenylmethane diisocyanate (MDI).
 9. The compositionaccording to claim 1, wherein the thermoplastic polyurethane has a Shorehardness in the range from 80 A to 100 A, determined in accordance withDIN
 53505. 10. The composition according to claim 1, wherein aproportion of the thermoplastic polyurethane in the composition is from30% to 75% by weight based on the overall composition.
 11. Thecomposition according to claim 1, wherein a proportion of the melaminecyanurate in the composition is from 25% to 35% by weight based on theoverall composition.
 12. The composition according to claim 1, wherein aproportion of the flame retardant (F2) in the composition is from 3% to15% by weight based on the overall composition.
 13. The compositionaccording to claim 1, wherein a proportion of the flame retardant (F1)is from 2% to 15% by weight based on the overall composition.
 14. Amethod of making a cable sheath, the method comprising: passing a corecomprising at least one wire through an extruder device; and coating thecore with a composition according to claim 1 during said passing.